Interpretive Summary: The LEPA (Low Energy Precision Application) sprinkler irrigation method has proven to be highly efficient in row crop irrigation where the water is applied at high rates and can be temporarily stored in basins between the rows for later infiltration. LEPA irrigation has not been evaluated, however, with closely spaced crops such as wheat that are usually planted on flat ground and have little temporary water storage capacity. To provide a controlled evaluation of LEPA irrigation of wheat, LEPA double-ended-sock and LEPA bubble sprinkler methods were compared with overhead spray irrigation using six different irrigation regimes. Wheat grain yields increased 15 bushels per acre for each 33% increase in irrigation amount and were determined to be significantly different statistically. The first year, yields with the two LEPA sprinkler methods were slightly higher than with the overhead spray method, and the second year they were slightly lower. For practical application, there was no benefit to using the LEPA irrigation methods for winter wheat in comparison to overhead spray irrigation. The information from this study can be used by growers to prevent installation of costly LEPA irrigation equipment for irrigation of winter wheat only.

Technical Abstract:
The yield response of winter wheat to LEPA double-ended-sock, LEPA bubble and overhead spray sprinkler methods was measured in the Southern High Plains of the USA with four irrigation amount and two irrigation timing treatments. Irrigation amounts ranged from zero to 100% of soil water replenishment in 33% increments. Irrigation timing was evaluated with the 100% irrigation amounts but with spring irrigation either delayed until booting or terminated early during early grain filling. The cropping years were 1993-94 and 1994-95, the wheat variety was TAM-202, the soil was Pullman clay loam and irrigations were applied with a lateral move irrigation system. Grain yields did not vary significantly among the three sprinkler methods during either year. For each 33% increase in irrigation amount, grain yields increased a statistically significant 1 Mg/ha in 1994, but significant yield increases occurred only for the first two irrigation amount increments in 1995. Only the irrigation timing treatment with earl termination of irrigation in 1994 utilized irrigation water more efficiently than the comparable 67% irrigation amount treatment. Deficit sprinkler irrigation as a percent of evapotranspiration was as effective as deficit irrigation based on plant growth stages and required less management skill. LEPA and spray irrigation were equally efficient for irrigation of winter wheat in the Southern High Plains.